5850's on top of each other in UD3R

you'll see a slight decrease in performance, but it shouldn't be too bad (1-4% or so)

If that is what it says, then that is what you have to do. If you want x16 and x16 you need to put it in these slots. I believe the other slots run at x8 speed and share that bandwidth with the other x16's. So if the first x16 slot and first x8 slot are populated they will both run at x8 speed. Is you put the 2nd card in the 2nd x8 slot it will only run at x8 speed even if the 2nd x16 slot is not populated.

Here is the specifications for the PCIe slots:

2 x PCI Express x16 slots, running at x16 (PCIEX16_1/PCIEX16_2) (Note 1)
2 x PCI Express x16 slot, running at x8 (PCIEX8_1/PCIEX8_2) (Note 2)

(Note 1) For optimum performance, if only one PCI Express graphics card is to be installed, be sure to install it in the PCIEX16_1 slot; if you are installing two PCI Express graphics cards, it is recommended that you install them in the PCIEX16_1 and PCIEX16_2 slots.

(Note 2) The PCIEX8_1 and PCIEX8_2 slots share bandwidth with the PCIEX16_1 and PCIEX16_2 slots espectively. When PCIEX8_1 is populated with an expansion card, the PCIEX16_1 slot will operate at up to x8 mode; when PCIEX8_2 is populated with an expansion card, the PC IEX16_2 slot will operate at up to x8 mode

looks like with a gpu in slot 1 (PCIEX16_1) and slot 3 (PCIEX8_1) will result in x8 - x8

If the cards are on top of each other, won't the cards malfunction due to the heat that is being produced?

From what I'm reading only with the first 2 slots are running at x16.
Slots 3 & 4 are x8 and they share with the first two slots so if you put the cards in 1 & 3 both will be operating at x8. I believe the performance hit should be minor with x8 and an HD5850 but you may want to put the second in slot 4 instead so the first card will still be x16.

Yes they will get hot. My asus motherboard is setup like this and I tried to CF 4870's. The top card would overheat because I didn't have enough air circulation between. These are the issues with dual card setups. Some motherboards drop some PCI-E slots to add an extra slot between the (2) x16 slots. This is a great help but you have to remember this when you are buying up front. Since the x58 chipset supports tri-SLI and i believe up to 4 ATI cards, they try and maximize the options leaving less space. There are few x58's that have the extra space. The Asus Deluxe does this but you can't run 3 cards unless the one 2nd is a single slot. http://usa.asus.com/product.aspx?P_ID=1H6537GW0fPVHNhO&...



The slot alternate.

Slot1 = PCI-E 16_1
Slot2= PCI-E 8_1
Slot3= PCI-E 16_2
Slot4 = PCI-E 8_2